International travel poses multiple challenges to the control of HIV in the US and worldwide. US residents may acquire HIV abroad and introduce infection into local networks not previously affected. HIV-seropositive US residents may transmit HIV to others while traveling. Transmission of antiretroviral (ARV) drug resistance is also of concern. High treatment levels in the US raise the specter of spreading ARV drug resistance worldwide, an outcome particularly worrisome to developing countries with limited second-line treatment options. HIV transmission risk may be compounded in foreign settings by destination-specific information, differing motivation and additional behavioral skills that are necessary for risk reduction behaviors while traveling internationally. International travel creates a change in environment that may facilitate behavioral disinhibition and lead to increased levels of high-risk behavior and substance use. The community of men who have sex with men (MSM) in San Francisco and the greater Bay Area represents a population with a high degree of international travel, along with a high prevalence of HIV, high ARV coverage and a high level of ARV drug resistance. Our study proposes to measure transmission risk of HIV and ARV drug resistance in the population of seropositive MSM who travel internationally. The specific aims are: 1) to measure the prevalence of sexual risk behavior among HIV-seropositive MSM during international travel;2) to document the prevalence of ARV drug resistance among MSM international travelers;and 3) to examine the informational, motivational and behavioral skills correlates of safer sex disinhibition during international travel. Our study will employ a mixed-methods approach combining quantitative and qualitative components to assess sexual risk behavior and potential correlates of behavioral disinhibition, organized according to the Information- Motivation-Behavioral Skills (IMB) model of HIV behavior change. We will use Respondent-Driven Sampling (RDS) to recruit a representative cross-sectional survey of 500 HIV-seropositive MSM in San Francisco and the greater Bay Area who traveled internationally in the past 12 months. We will obtain population-based estimates of unprotected anal intercourse and ARV drug resistance prevalence (Aims 1 and 2). HIV risk behavior data will be collected through quantitative questionnaires and qualitative interviews regarding both the individual and destination-specific informational, motivational and behavioral skills components that may affect safer sex disinihibition while traveling internationally (Aims 1, 2, and 3). Public health relevance: Our study design will provide data on individual characteristics that may influence HIV risk behavior across situations, as well as destination-specific attributes that influence behavior while visiting particular locations. Ultimately, our study will contribute to the development of prevention strategies specifically addressing the correlates of behavioral disinhibition associated with cross-border HIV transmission and spread of ARV drug resistance in an era of expanding treatment worldwide.